1. Field of the Invention
The present invention relates in general to centrifugal separators and in particular to a method and apparatus for preventing the accumulation of centrifugally separated solid contaminant matter at the outlet passages in such separators.
2. Description of the Prior Art
Pitot pumps are a form of centrifugal pump and typically include a hollow rotatable casing disposed within a surrounding housing, means for delivering a fluid to be pumped to the casing, and a pitot tube fixed with respect to the casing for collecting fluid at a desired point in the casing spaced from its rotational axis. Such pumps also include a discharge sytem for receiving fluids from the pitot tube and for discharging the same at a desired pressure coaxially of the casing. Such pitot pumps are illustrated in U.S. Pat. Nos. 3,795,459; 3,817,659; and 3,838,939, all of which are owned by the assignee of the present invention.
One use of pitot pumps is to supply pressurized fluid to a hydraulic pump located in the bore of an oil well for pumping oil out of the well into a suitable collection facility. In such an application, the fluid may be a portion of the oil produced from the well itself. Very often, however, the oil taken from the well contains contaminants which tend to wear and damage the pump. It has, therefore, been proposed to construct a pitot pump to function as both a pump and as a centrifugal separator, in which contaminants are removed from the oil as the oil is pumped. Such a pump is illustrated in U.S. Pat. No. 3,817,446.
Experience with pitot pumps-separators of this type has shown that sand and other solid or heavy viscous contaminants in the fluid tend to accumulate on the inner surface of the rotatable casing. Ducts or orifices are provided around the periphery of the casing to discharge the contaminants from the casing separately from the discharge of the fluid. However, the accumulation of contaminants on the inner surface of the casing often causes the ducts or orifices to become clogged or plugged. Such clogging of the contaminant discharge orifices is a major problem in centrifugal separators.
U.S. Pat. No. 4,036,427 discloses a combination pitot pump and centrifugal separator wherein a stationary stirrer vane assembly is utilized to prevent the build-up of contaminant matter on the inner surface of the rotatable casing. The vane assembly extends into close proximity to the casing inner surface, generating turbulence in the outermost extent of the casing to dislodge accumulated contaminant matter. The outer end portion of the vane assembly can be constructed to direct a jet of relatively clean fluid toward the inner surface of the rotatable casing. However,the relatively high speed of the contaminant containing fluid moving past the vane causes a high rate of wear at the end of the vane in these prior art devices.